The present invention relates to a counterbalancing shaft accommodating structure which is suitable for use in a motor vehicle engine.
There has been known a technique which uses counterbalancing shafts as one of techniques for absorbing vibrations of a reciprocating engine (hereinafter, referred to simply as an engine).
In addition, there has also been known a structure in which the counterbalancing shafts are provided within an oil pan which is provided on a lower side of the engine, and a structure like this is disclosed in JP-A-2005-36872 below.
However, when the counterbalancing shafts are provided within the oil pan, there occurs a situation in which the counterbalancing shafts stir oil within the oil pan. As this occurs, there may appear a situation in which a phenomenon is caused in which air bubbles are generated in oil (so-called aeration) or a loss of drive torque of the engine is caused.
Incidentally, in the technique in JP-A-2005-36872, as is shown in FIG. 4 of the same document, a structure is disclosed in which balance shafts (counterbalancing shafts) (44, 45) are accommodated within an upper housing (42) and a lower housing (43).
A plurality of openings (to which no reference numeral is imparted) are formed in the upper and lower housings (42, 43) in the technique of JP-A-2005-36872. Namely, it is not that the upper and lower housing (42, 43) are sealed hermetically.
Because of this, in the technique of JP-A-2005-36872, even though the balance shafts (44, 45) are accommodated within the upper and lower housings (42, 43), oil flows into the interior of the upper and lower housings (42, 43), and the oil continues to be stirred by the balance shafts (44, 45), leading to a problem that the aeration of the oil or the torque loss is caused.
In addition, in general, the use of counterbalancing shafts increases the size of an engine. Note that in the technique of JP-A-2005-36872, although the engine is considered to be made small in size to some extent by providing the balance shafts (44, 45) within the oil pan, there are still demands for smaller engines.